1. Field of the Invention
The present invention relates to a pellicle for lithography used for dustproof protection of a mask for lithography used in lithography for forming a fine pattern, and a method for producing it, especially to a large-sized pellicle for lithography used when a liquid-crystal display panel is manufactured.
2. Description of the Related Art
A pattern is formed by exposing a semiconductor wafer or a liquid crystal substrate with light in manufacture of semiconductor such as LSI, VLSI, or the like, or manufacture of a liquid-crystal display panel. In this case, if dust has adhered to an exposure original plate (a mask for lithography) to be used, the dust absorbs light or bends light. Thus, an transferred pattern may be deformed, or an edge may be rough, and also the ground may be soiled to be black, resulting in degradation of a dimension, a quality, and an appearance or the like, which may lead to a problem of a lowering of performance or production yield of a semiconductor device, a liquid-crystal-display panel, or the like.
For this reason, these works are usually done in a clean room. However, since it is difficult to always keep an exposure original plate clean even in the clean room, there is adopted a method of attaching a pellicle for dustproof protection which transmits the light for exposure to the surface of the exposure original plate. In this case, dust does not adhere directly to the surface of the exposure original plate but adheres to the pellicle film. Accordingly, if the focus is on the pattern of the exposure original plate at the time of lithography, the dust on the pellicle film does not affect the transfer.
Such a pellicle fundamentally consist of a pellicle film produced by applying an application liquid which consists of a cellulose nitrate, a cellulose acetate or the like, through which light used for the exposure is transmitted well, to a smooth substrate by a spin coat method, drying the solvent in this application liquid, and peeling a transparent film formed on the substrate from the substrate, and a pellicle frame made of aluminium alloys, such as A7075 subjected to black alumite treatment, stainless steel, polyethylene, or the like, which are adhered by applying a good solvent for the pellicle film to one end face of the frame, and then air-drying it to adhere them (for example, see Japanese Patent Application Laid-open (kokai) No. 58-219023), or being adhered with adhesives, such as an acrylate resin, an epoxy resin or the like (for example, see U.S. Pat. No. 4,861,402 specification or Japanese Patent publication (kokoku) No. 63-27707). Furthermore, the pellicle has a sticking layer for attaching the pellicle to an exposure original plate, made of a polybutene resin, a polyvinyl acetate resin, an acrylate resin, or the like and formed on another end face of the pellicle frame, and a reticle sticking layer protection liner for protecting the reticle sticking layer.
In recent years, a pellicle has come to be used also in a lithography process in processes for production of a liquid-crystal display panel or the like. In this case, as a pellicle to be used, a pellicle with a very large size as 1000 cm2 or more is needed in the case of a one-time exposure formula according to a mirror projection method or the like, as compared with those used in the semiconductor production process (750 cm2 or less, one having a diameter of 12 inch at the largest is practically used). The spin coat method had been conventionally used as a production method of the pellicle film also in the case of a pellicle with such a large size.
However, when the spin coat method is used as a method for producing a pellicle film with a large size as, for example, 1000 cm2 or more, there were the following problems: 1) It is necessary to use a quite large amount of application liquid to be applied on the substrate. Almost all the application liquid is shaken off during rotation, and does not remain as an application liquid film. Therefore, it is quite wasteful, and a manufacturing cost is increased; 2) When the film is formed on a large-sized substrate by the spin coat method, unevenness of a film thickness is increased (for example, a film thickness distribution in plane is over ±10%), and a light transmission is lowered. Therefore, the pellicle film with a sufficient performance cannot be obtained; 3) It is difficult to rotate a large substrate, and it is a problem to rotate the large and heavy substrate at high rate. Therefore the manufacturing cost becomes high. Especially important problems are the problems 1) and 2). When the pellicle film having a large size is actually produced by a spin coat method, there has been a problem that optical characteristics which the pellicle film should have essentially can be hardly obtained.